Pharmacovigilance Evidence Review: Rare blood clots with AstraZeneca COVID-19 vaccine in women under 55

6 April 2021

Rare blood clots with AstraZeneca COVID-19 vaccine in women under 55

The DSRU has evaluated all publicly available data on blood clotting incidents after immunisation with the AstraZeneca COVID-19 vaccine and has concluded there is evidence consistent with a causal link between the vaccine and rare blood clots in women aged under 55.

The DSRU is sharing its rapid pharmacovigilance assessment with regulatory authorities in Europe and the UK and will seek publication in a peer-reviewed scientific journal.

Its ‘living evidence review’ found events of thrombosis (blood clotting inside the arteries) with thrombocytopenia (a reduction in blood platelets that usually causes bleeding but in rare cases actually results in clotting) in women under 55 were consistent with a causal link to the AstraZeneca vaccine.

But it stressed these events were rare. In the UK, as of March 24, 30 events had occurred resulting in seven deaths, from 18.1million doses of vaccine.

The researchers analysed data from Germany. The analysis suggests there was one event of cerebral venous thrombosis for every 46,512 women vaccinated, while there has been one female death associated with this condition for every 149,860 vaccine doses given to women. These reporting rates are for all women who received the AstraZeneca vaccine in Germany, not just women under 55.

For context, in the UK, it has been calculated that 47,000 COVID-19 vaccines prevent one death from COVID-19 among all people under 50.

Professor Saad Shakir, Director of the DSRU, said: “The AstraZeneca vaccine is safe and effective. It has protected millions of people from Covid-19 and will continue to do so around the world.

“Data from regulatory authorities in Europe show a rare but serious side effect in women below the age of 55. There is no evidence to support stopping the vaccine in men of any age. Risk minimisation measures should be put in place for women below 55 years.

“Work is underway by scientists in Europe and the UK, regulatory authorities and health service bodies to evaluate the totality of the data to better understand the biological, clinical and epidemiological characteristics of these rare clotting with thrombocytopenia events. The aim is to inform risk minimisation plans to ensure an optimal benefit risk balance for all users.”

The DSRU is an independent and internationally renowned research unit that monitors, studies and communicates the safety and risk management of medicines.

Separately to this research, the DSRU is monitoring the safety and effectiveness of the AstraZeneca vaccine by enrolling 10,000 UK vaccinees and proactively asking them questions about possible side effects.  No blood clotting side effects have been recorded, but the study is at its early stages.